Fuel cells convert gaseous fuels (fuel and oxidant) via an electrochemical process directly into electricity. Generally, the electricity-generating reaction within the fuel cell is exothermic resulting in a temperature increase of the cell. Even though the fuel cell is run at elevated temperature, this temperature increase can reduce fuel cell efficiency and cause thermal runaway, and means for cooling the fuel cell are invariably required.
One method of cooling a fuel cell involves the use of a coolant which is circulated in thermal exchange with the cell. Heat absorbed by the coolant is discharged away from the fuel cell by sensible heat and may be rejected from the system by use of heat exchangers. The coolant may then be recycled to the cell. As an embodiment of this general approach a fuel cell may be cooled by supplying the fuel cell with more oxidant (e.g. air) than is actually required for power generation, the excess oxidant serving as a coolant. However, this approach requires specific cooling circuitry within the fuel cell system and/or an increase in size of passages within the fuel cell to facilitate adequate coolant flow. This also typically requires the use of large fans/compressors and this can result in increased parasitic power losses. These factors result in an increase in the size and complexity of fuel cell systems and an increase in overall expense, particularly where large and/or numerous heat exchangers are called for. Additionally, where the gaseous feed to the fuel cell is used as coolant, the excess flow rate required can lead to increased pressure losses within the system.